Photographic and Acoustic Techniques Applied to a Study of the Side Aspect Target Strength of Free-Swimming Fish

AbstractA major criterion for permitting the deployment of tidal turbines in Washington State’s Puget Sound is management of risk of injury to killer whales from collision with moving turbine blades. An active monitoring system is being proposed to detect and track killer whales within proximity of turbines and alert turbine operators of their presence and location to permit temporary turbine shutdown when the risk of collision is high. Knowledge of the target strength (TS) of killer whales is critical to the design and application of active acoustic monitoring systems. In 1996, a study of the TS directivity of a 2.2-m-long bottlenose dolphin at an insonifying frequency of 67 kHz was performed. Noting that killer whales, which are dolphins, are morphologically similar to bottlenose dolphins and then assuming allometry, we estimated the relative broadside and tail aspect TS of a 7.5-m-long adult killer whale at an insonifying frequency of 67 kHz to be −8 and −28 dB, respectively. We used a three-layer model for plane wave reflection of sound at 200 kHz from the lung of killer whales to estimate their TS. We assessed the accuracy of our killer whale TS estimates by comparing them with TS estimates of free swimming killer whales obtained using a split-beam active acoustic system operating at 200 kHz. The killer whale TS estimates based on the preliminary model were in good agreement with those obtained for free swimming killer whales.

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Hydroacoustic target strength vs. fish length revisited: Data of caged, free-swimming European whitefish (Coregonus lavaretus L.) suggest a bi-phasic linear relationship under a limited range of tilt angles

Fisheries Research ◽

10.1016/j.fishres.2020.105620 ◽

2020 ◽

Vol 229 ◽

pp. 105620

Author(s):

Josef Wanzenböck ◽

Jan Kubecka ◽

Zuzana Sajdlova ◽

Jaroslava Frouzova

Keyword(s):

Linear Relationship ◽

Limited Range ◽

Target Strength ◽

Fish Length ◽

Coregonus Lavaretus ◽

Free Swimming

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Single-target echo detections of jellyfish

ICES Journal of Marine Science ◽

10.1016/j.icesjms.2003.12.008 ◽

2004 ◽

Vol 61 (3) ◽

pp. 383-393 ◽

Cited By ~ 41

Author(s):

Andrew S Brierley ◽

Bjørn Eric Axelsen ◽

David C Boyer ◽

Christopher P Lynam ◽

Carol A Didcock ◽

...

Keyword(s):

Target Strength ◽

Published Data ◽

Acoustic Survey ◽

Free Swimming ◽

Survey Techniques ◽

Single Target ◽

Acoustic Target ◽

Frequency Identification ◽

Jellyfish Species ◽

Chrysaora Hysoscella

Abstract Acoustic target-strength (TS) measurements are presented for tethered and free-swimming individual Chrysaora hysoscella (Scyphozoa) and Aequorea aequorea (Hydrozoa) medusae in Namibian waters. Tethered individual C. hysoscella (17–54 cm total umbrella diameter) and A. aequorea (19–28 cm total umbrella diameter) were ensonified at 38 kHz using a portable echosounder. Mean TS values for individual medusae at this frequency ranged from −67.3 to −52.8 dB for C. hysoscella and from −65.4 to −50.1 dB for A. aequorea. There was a positive relationship between medusa diameter and TS for both species. TS of individual medusae varied cyclically over time by about 15 dB, probably because of the periodic contraction of the medusae whilst swimming. C. hysoscella was parasitized by hyperid amphipods (maximum infestation >1800 parasites per medusa). A fluid-cylinder scattering model was used to determine the expected backscatter from the parasites, and it suggested that even at the highest observed level of infestation the jellyfish itself remained the major contributor to total backscatter at 38 kHz. Single-target echoes from targets identified by trawling as medusae were obtained from vessel-mounted echosounders at 18, 38, 120, and 200 kHz. Triangulation between echosounder beams to identify targets detected simultaneously at all four frequencies increased confidence that echoes were in fact from single targets. The 38-kHz TS values from free-swimming medusae corresponded with values obtained from tethered animals at the same frequency, providing strong evidence that the TS estimates were robust. TS values at all four frequencies (Chrysaora hysoscella mean umbrella diameter 41 cm, TS at 18 kHz = −60.0 dB, 38 kHz = −65.5 dB, 120 kHz = −68.0 dB, and 200 kHz = −70.5 dB. Aequorea aequorea mean inner-umbrella diameter 6.5 cm, TS at 18 kHz = −66.0 dB, 38 kHz = −65.5 dB, 120 kHz = −68.0 dB, and 200 kHz = −73 dB) were consistent with previously published data. Given these robust TS estimates, the possibility may now exist for multi-frequency identification and evaluation of these jellyfish species in some circumstances, and for the use of acoustic-survey techniques to estimate jellyfish abundance.

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Estimating the target strength of live, free-swimming chokka squid Loligo reynaudii at 38 and 120 kHz

ICES Journal of Marine Science ◽

10.1093/icesjms/fsq058 ◽

2010 ◽

Vol 67 (7) ◽

pp. 1381-1391 ◽

Cited By ~ 3

Author(s):

Michael A. Soule ◽

Ian Hampton ◽

Marek R. Lipiński

Keyword(s):

Ex Situ ◽

Target Strength ◽

Research Vessel ◽

Free Swimming ◽

Spawning Aggregations ◽

Backscattering Cross Section ◽

In Situ Experiments ◽

In The Wild ◽

Loliginid Squid

Abstract Soule, M. A., Hampton, I., and Lipiński, M. R. 2010. Estimating the target strength of live, free-swimming chokka squid Loligo reynaudii at 38 and 120 kHz. – ICES Journal of Marine Science, 67: 1381–1391. Estimates of the target strength (TS) of the loliginid squid Loligo reynaudii at 120 kHz were made from ex situ experiments on 38 caged, but free-swimming animals, and at 38 and 120 kHz from 17 in situ experiments on spawning aggregations in the wild conducted from a research vessel and from small boats. The cage experiments suggested that the backscattering cross section is proportional to mantle length (ML), which would not be expected from simple considerations of ML in relation to wavelength. A similar relationship was found during the in situ experiments conducted from the research vessel. The TS estimates from the research vessel agreed well with those from the cage experiments, for both of the two methods used to extract squid TS distributions from the overall TS distributions, but were some 2–3 dB lower than those from the small boats. This suggests that in situ estimates are affected by the vessel and/or the way in which squid react to it. It is concluded that ex situ experiments on L. reynaudii TS are of most value as a complement to in situ experiments, which should be made concurrently while surveying, using systems capable of having higher volume resolution than in the current experiments, to maximize the applicability of the estimates to the survey data.

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Laboratory target strength measurements of free-swimming Antarctic krill (Euphausia superba)

The Journal of the Acoustical Society of America ◽

10.1121/1.423077 ◽

1998 ◽

Vol 103 (6) ◽

pp. 3268-3280 ◽

Cited By ~ 12

Author(s):

Timothy Pauly ◽

John D. Penrose

Keyword(s):

Antarctic Krill ◽

Euphausia Superba ◽

Target Strength ◽

Free Swimming ◽

Antarctic Krill Euphausia Superba

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The time course of calcium deposition in shells of the barnacle (Balanus amphititre amphititre) during cyprid-juvenile metamorphosis

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100168621 ◽

1994 ◽

Vol 52 ◽

pp. 178-179

Author(s):

Nancy R. Wallace ◽

Craig C. Freudenrich ◽

Karl Wilbur ◽

Peter Ingram ◽

Ann LeFurgey

Keyword(s):

Electron Microscopy ◽

Scanning Electron Microscopy ◽

Time Course ◽

Vertical Plane ◽

Mantle Cavity ◽

Qualitative Assessment ◽

Calcium Deposition ◽

Free Swimming ◽

Freeze Dried ◽

Scanning Electron

The morphology of balanomorph barnacles during metamorphosis from the cyprid larval stage to the juvenile has been examined by light microscopy and scanning electron microscopy (SEM). The free-swimming cyprid attaches to a substrate, rotates 90° in the vertical plane, molts, and assumes the adult shape. The resulting metamorph is clad in soft cuticle and has an adult-like appearance with a mantle cavity, thorax with cirri, and incipient shell plates. At some time during the development from cyprid to juvenile, the barnacle begins to mineralize its shell, but it is not known whether calcification occurs before, during, or after ecdysis. To examine this issue, electron probe x-ray microanalysis (EPXMA) was used to detect calcium in cyprids and juveniles at various times during metamorphosis.Laboratory-raised, free-swimming cyprid larvae were allowed to settle on plastic coverslips in culture dishes of seawater. The cyprids were observed with a dissecting microscope, cryopreserved in liquid nitrogen-cooled liquid propane at various times (0-24 h) during metamorphosis, freeze dried, rotary carbon-coated, and examined with scanning electron microscopy (SEM). EPXMA dot maps were obtained in parallel for qualitative assessment of calcium and other elements in the carapace, wall, and opercular plates.

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